C : $686
Work Step by Step
Since $300 $$ worth of merchandise was returned, the remaining amount to be repaid was 700. The conditions of the trade was that 2/10, meaning a 2% discount if the money is repaid withing 10 days. They repaid the money withing 10 days, so they get a 2% discount on 700. That means the final amount to be repaid was (0.98 x 700) = 686.